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Math Help - Related Rates question 5

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    Exclamation Related Rates question 5

    Each edge of a cube is expanding at a rate of 4cm/s.

    a) How fast is the volume changing when the edge is 5cm?
    b) at what rate is the surface area changing when the edge is 7 cm?
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    Rhymes with Orange Chris L T521's Avatar
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    Quote Originally Posted by math123456 View Post
    Each edge of a cube is expanding at a rate of 4cm/s.

    a) How fast is the volume changing when the edge is 5cm?
    b) at what rate is the surface area changing when the edge is 7 cm?

    If s is the length of one side of a cube, then its volume is V=s^3. We are looking for \frac{\,dV}{\,dt}, so that means that V=s^3\implies\frac{\,dV}{\,dt}=3s^2\frac{\,ds}{\,d  t}

    You know the rate at which s is changing, and you know the length of the side at that instant in time. Do you think you can complete the problem now?
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